What could be more frightening to a parent than watching a child experience a febrile seizure, which commonly includes losing consciousness and shaking? Yet nearly one in every 25 children has at least one febrile seizure at some point, while more than a third of these children will have additional febrile seizures before they outgrow the tendency.

Commonly, the seizures occur between the ages of 6 months and 5 years. Although distressing to parents, febrile seizures are not associated with any ongoing health issues. Now, new research from Canada has shown how the combined measles–mumps–rubella–varicella (commonly referred to as the MMRV) vaccine shows a slightly increased risk of febrile seizures in children, compared with the previously separate vaccines for MMR and varicella (chickenpox). “Potential benefits must be balanced by the increased risk (albeit small) of febrile seizures with the combination vaccine,” wrote the authors in their study published today in Canadian Medical Association Journal.

Combination MMRV vaccines were developed as an alternative to separate MMR and chickenpox vaccines. Public health officials thought that a reduction in the number of needles received by young children would eliminate pain for them and anxiety for their parents; as a consequence, this might boost vaccination coverage levels while decreasing costs. Currently, two vaccines, with different formulations, are available in North America: ProQuad (Merck) is used primarily in the U.S., whereas Priorix-Tetra (GlaxoSmithKline) is primarily used in Canada. Vaccine safety studies of ProQuad have identified a slightly increased risk of febrile seizures in children after the first dose (given between the ages of 12 to 23 months), but not after the subsequent preschool dose. Similarly, studies of Priorix-Tetra have found it to be as safe as the two separate vaccines, except for a higher incidence of fever.

To determine whether there is an increased risk of febrile seizures from the combined vaccine, researchers looked at data on 227,774 children between the ages of 12 and 23 months who had received either the MMRV vaccine or the MMR plus a separate chicken pox vaccine between 2006 and 2012 in Alberta, Canada.

After analyzing the data, the researchers found a slight increase in the relative risk of febrile seizure with the MMRV vaccine compared with the MMR+V vaccine — about one excess seizure for every 2,841 doses. The researchers noted that, although this rate is double that of the two separate vaccines, the absolute risk is relatively small. Plus, their findings are consistent with the results of a study of the U.S. version of the vaccine. For these two reasons, they suggest counseling parents about the risk of fever and, when necessary, recommending fever medication to alleviate any symptoms.


Source: MacDonald SE, Dover DC, Simmonds KA, Svenson LW. Risk of febrile seizures after first dose of measles–mumps–rubella–varicella vaccine: a population-based cohort study. Canadian Medical Association Journal. 2014.